This invention relates to motion pictures and to the film transport movement therefor in cameras and projectors, and particularly in cameras using wide 65 mm film as it is distinguished from 35 mm film. Heretofore, the Fox camera movements have been characterized by a single film transport claw engageable with perforations along one side of the film, and by register pins engageable with perforations along the other or both sides of the film. Although the single claw camera movements have been satisfactory in the transport of 35 mm film, difficulties arise in single claw camera and projector movements used in the transport of 65-70 mm film. The wide film is not as stable due to its thickness to width ratio, its greater width and transport dimensions giving rise to problems in claw engagement and registration, and its double size proportionately multiplies problems with respect to the physical properties of the film per se; for example the strength, and any deformations thereof. It is commercially available film with which this invention is primarily concerned, and especially wide 65-70 mm motion picture film with perforated drive margins in a body of acetate or Mylar having 0.003 to 0.006 inch thickness, and carrying an 0.0008 inch thick photographic emulsion on the forward side thereof.
This invention is an improvement over the "Fox" camera movement that has been successfully used to intermittently pull down and register film for the exposure of successive frames or pictures. This type of movement is characterized by a cam incorporated in a driven crank member that oscillates an arm. The arm swings on a pivot so that its radius strikes an arc coincidental with an arcuate film guideway, and the end of the arm carries a retractile claw shifted radially into and out of engagement with the perforations along one side of the film by said cam. A second cam shifts register pins into and out of anchored engagement with the perforations at the other or both sides of the film. Characteristically, the two cams are spaced on the single crank member, one cam in alignment with the perforations along one side of the film, and the other cam centered with respect to the film plane and disposed between the crank member and bearing support therefor. These positions and relationships are well established and dictated by the length of the claw arm that overlies its cam, by the locations of the register pin mechanism, and by other quite necessary features including claw adjustment and retraction of the registration pins. It is to be understood that this type of camera movement is made with precision in order to have reliability and smoothness of operation, and to this end the oscillating parts are light weight as compared to the heavy supporting mass that has been necessary in the surrounding frame or base. In this latter respect, difficulties have existed in balance, and vibration has always been a problem.
Convention has dictated top to bottom or "pull down" transport of motion picture film, and consequently the horizontal picture format extends transversely of the film. With the advent of larger projection screens and wide angle showing of motion pictures, the resolution afforded by 35 mm film is lacking and resort has been made to the larger format available with 65-70 mm film. It will be readily seen that 65-70 mm film produces four times the format area when projected in the vertically disposed "pulldown" mode, and that it will produce eight times the format area if projected in a horizontally disposed "pull-across" mode. For example, the horizontal transport of film as it is shown herein has a frame format of approximately 2 inches by 2.75 inches. Accordingly, the size of the camera movement as it is disclosed herein is proportionately larger than the conventional 35 mm mechanism, and it requires 2.799 inches of claw movement and registration of a commensurate length of film per frame; an increase from four to fifteen perforations. It is a general object of this invention to provide a practical film transport movement for cameras and projectors, by which wider films can be successfully advanced and registered frame by frame, while meeting all requirements of access, adjustment, accuracy and reliability.
This film transport movement employs the Fox principle of an oscillating transport arm carrying a retractile claw controlled by a cam, it being an object of this invention to provide this principle to engage both sides of the perforated film and thereby balance the driving forces applied during transport. With the present invention there is a transport arm and retractile claw controlled by a cam at each side of the film, and a transmission therewteen. In practice, there is a transmission housing that exposes the two cams in alignement with the two opposite rows of film perforations to be engaged by the claws associated therewith. The transmission housing accommodates a pulley driven crank shaft rotatably carried therein on anti friction bearings.
With the transmission intermediate the transport arms as above described, there is a wide separation of the top and bottom cams and of the top and bottom transport arms complementary thereto. It is an object of this invention to provide for locked adjusted alignment of these two transport arms so as to ensure that they move together with driving engagement from separate crank pins on a common axis eccentric from the common cam rotation axis. It is also an object of this invention to provide for locked pitch adjustment of these two transport arms in said locked alignment, allowing for film shrinkage and so as to ensure proper claw position with respect to the frame aperture. These two adjustment and locking features are incorporated in a shiftable pivot post and cam positioned carriage therefor. The pivot post is comprised of separable and concentric members with separate lock screws for the alignment and the pitch adjustment functions.
The pivot post, transport arm and crank drive therefor are offset downward and/or to one side in the direction of film transport; down and/or to one side of the film exposure aperture. Consequently, the space behind the aperture plate is open for light transmission in projectors, and for accomodating mechanism in a camera as herein disclosed. It is an object of this invention to reserve this space rearward of the aperture plate for either of said uses, while providing an offset drive to the aforesaid transmission with simultaneous timed extension and retraction of register pins. In practice, the offset drive is spaced rearward from the aperture plate and the register pins are located along the bottom margin of the film to engage the perforations therealong. It is an object of this invention to engage register pins at both the front and back of each film frame when it is being exposed, thereby ensuring a positive longitudinal and vertical location of the film, flatness being maintained by a vacuum back plate behind the film.
Retraction of both the transport claw pins and register pins is quite necessary for loading and unloading the film; that is, insertion into and removal of film from the guideway. Also, secure tranport engagement of the claw pins and of the register pins is exceedingly important with this large film format, and accordingly it is an object of this invention to double or more than double the shear strength of said claw pins and register pins. With the present invention, compared to the Fox movement, the shear strength of the transport claw pins is four times greater than a single claw pin, there being two pairs of claw pins; and the shear strength of the register pins is two times greater than a pair of pins engaging opposite perforation. It is significant that the present invention provides longitudinal spaced pairs of pins between which the exposed film section is extended in flat condition for registration. Normally, either the claw pins or the register pins are projected to engage the film perforations, and retraction of the register pins is provided for when the claw pins are also retracted through rotative positioning of the movement.
Shutter speed is a controlling factor in motion picture taking, and the present standard of 24 to 48 frames per second involves synchronously timed rotary and oscillatory and reciprocating motions of various means. Due to the increased size of this transport and register movement for the larger 65-70 mm film, vibration is a factor to be considered. Accordingly, it is an object of this invention to counterbalance the motion of oscillatng and reciprocating members, with counter motion of other members. As will be described, a counterbalance arm and weight is disposed between and oscillates in opposition to the motion of the transport arms. A rotary drive helps to counterbalance the reciprocating motion of the register pins. And, all rotary members are counter balanced for smoothness and quiet operation.